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Etude théorique de l'excitation collisionnelle de l'ammoniac et de ses isotopomères deutérés dans le milieu interstellaire

Abstract : Observation and study of molecular clouds of the interstellar medium require knowledge of fundamental physical data that are given access to physical characteristics of this medium, notably temperatures and densities. These regions are not generally at the thermodynamic equilibrium and calculation of rotational levels populations, which are linked to physical characteristics of the interstellar matter, requires to take into account all the radiative and collisional processes that are populating these levels. Many works have been done on Einstein's coefficients and collisional rate coefficients of a number of molecules. For the collisional processes, major perturbers in the interstellar medium are H2, H and He.
New instruments, that will furnish excellent spatial and spectral resolution, will be at work in a near future. They are spatial observatory HERSCHEL and the milimetric interferometer ALMA. Interpretation of the future observations of these instruments will need to know with sufficient accuracy collision rate coefficients of molecules. Even more, rate coefficients of some molecules have to be determined for the first time.
Ammonia NH3, one of the major tools in the study of the molecular interstellar medium, has interested us and we have calculated rate coefficients for this molecule in collision with He and H2. We have benefited of the existence of new accurate intermolecular potential surfaces for NH3-He and NH3-H2. With the help of the molecular collision code MOLSCAT we determined collisional integral cross sections of these systems. These cross sections are used to calculate the collisional rate coefficients.
Deuterated isotopomers of ammonia NH2D, ND2H, and ND3 have been detected in the molecular interstellar medium. These discoveries happened recently for the doubly and triply deuterated isotopomers (2000 and 2003). Until today, there were no values of rate coefficients with helium for these species that were theoretically or experimentally determined. Because of the importance of deuterated molecules in the study of interstellar chemistry and its evolution, we have calculated the very first rate coefficients for deuterated isotopomers of ammonia in collision with helium and published the first results.
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Contributor : Léandre Machin <>
Submitted on : Tuesday, January 30, 2007 - 5:43:10 PM
Last modification on : Monday, December 14, 2020 - 9:48:23 AM
Long-term archiving on: : Wednesday, April 7, 2010 - 2:34:47 AM


  • HAL Id : tel-00128133, version 1


Léandre Machin. Etude théorique de l'excitation collisionnelle de l'ammoniac et de ses isotopomères deutérés dans le milieu interstellaire. Astrophysique [astro-ph]. Université Pierre et Marie Curie - Paris VI, 2006. Français. ⟨tel-00128133⟩



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